This application is a national phase application under 35 U.S.C. §371 of International Application No. PCT/EP2004/014882 filed 30 Dec. 2004, which claims priority to U.S. application Ser. No. 10/750,145 filed 31 Dec. 2003. The entire text of each of the above-referenced disclosures is specifically incorporated herein by reference without disclaimer.
The present invention relates to a process for making a coated optical article, in particular an ophthalmic lens, a lens blank or a lens mold, free of visible fining lines, and in particular for directly forming a functional coating, such as an anti-abrasion hard coating, onto a fined but unpolished main face of an optical article, whereby no fining lines are visible when the coated lens blank is illuminated with an arc lamp. This process may be designated as “press coating process”.
The main faces of an ophthalmic lens blank, such as a lens blank made of a transparent plastic material, are classically subjected to a surface mechanical treatment.
This mechanical treatment comprises a group of operations leading to the production of a lens blank whose main faces are perfectly polished and have the desired curvatures (optical powers).
The mechanical treatment typically comprises three successive steps: grinding, fine grinding (also called fining) and polishing.
Grinding is a mechanical processing step intended to create the curvature on the face of the lens blank.
Fine grinding (fining), performed after grinding further changes the geometry of the treated face of the lens blank but can lead to a translucent lens blank whose treated face still shows, significant surface roughness. Typically, the Rq of the fined face is above 0.1 μm, and preferably ranges from 0.05 to 1.5 μm, more preferably from 0.1 to 1.0 μm.
Finally, the polishing, a relatively long mechanical processing step, which does not change the geometry of the treated face, removes the remaining roughness as far as possible to give the final transparent lens blank. Typically, the surface roughness Rq of the polished face of the lens blank ranges under 0.01 μm, preferably around 0.005 μm.
Following the mechanical treatment, functional coatings such at primer coating, impact-resistant coating, anti-abrasion hard coating, anti-reflective coating and top coat are classically deposited on the mechanically treated main face of the lens blank.
Avoiding the cumbersome polishing step of the main face of the lens blank prior forming a functional coating on the main face of the lens blank would thus be a definitive advantage for both economy and environment.
U.S. Pat. No. 4,417,790 and international patent application WO 01/67139 disclose spin or dip coating a fined but unpolished main face of a lens. The coating thickness is at least more than 10 times higher than the surface roughness of the fined main face and in WO 01/67139 application the difference of value of the refractive indexes between the lens material and the coating material shall be less than 0.01. Although the resulting coating lens becomes transparent using such a coating thickness or refractive index matching, the fining lines on the lens main face, i.e. the lines resulting from the fine grinding processing step, remain visible in particular when the coated lens is illuminated by an arc lamp.
U.S. Pat. No. 6,562,466 discloses a process for transferring a coating onto a main face of a lens blank which comprises depositing a requisite amount of a curable glue on a main face of a lens blank, bringing a coating born by a flexible support in contact with the curable glue, applying a pressure to the flexible support to spread the glue and form a uniform layer of glue on the main face of the lens, curing the glue and withdrawing the support, whereby one recovers a lens blank having the coating adhering to the main face of the lens blank.
Although coated lens blank free of visible fining lines may be obtained with the above coating transfer process, the thickness of the final coating including the cured glue layer and the transferred coating is typically of 25 μm or more and the transferred coating comprises several layers of different chemistry.
Applicant has now found that it is possible to make a coated optical article, especially a lens blank, free of visible fining lines in which the coated main face of the article is merely fine grinded but not polished and even though the coating is a thin coating, for example has a thickness of 10 μm or less, and/or the refractive index difference between the coating and the article, in particular a lens blank, is high, for example is up to 0.05, even 0.1 or more.
Other classical spin, dip or flow coating cannot lead to an article free of visible fining lines when the article is illuminated by an arc lamp.